Resistor, and method for making same

ABSTRACT

A resistor includes a substantially cylindrical resistive element having a resistance of less than about 1 mΩ, a substantially cylindrical first termination electrically connected to the resistive element and a second termination electrically connected to the resistive element. The substantially cylindrical first termination is hollow to allow for accepting a connection such as from a battery cable. In addition there may be sense leads present on the resistor. A method of forming a substantially cylindrical resistor includes forming a hollow cylindrical resistor body by rolling a flat sheet comprising a resistive element and a first termination and a second termination joined on opposite ends of the resistive element.

FIELD OF THE INVENTION

The present invention relates to resistors, particularly resistors inautomotive and related applications.

BACKGROUND OF THE INVENTION

As electronics content in a typical vehicle has substantially increased,the demands on the battery and charging system of a typical vehicle havealso increased. Moreover, with the advent of the hybrid gas-electric carand all-electric cars the battery and charging system becomes anevermore vital part of a vehicle. An unhealthy electrical system intoday's car can jeopardize vital functions such as steering and braking.

Therefore, it has become essential for onboard computers to have sensoryinformation about the charge used, charge returned and charge availablefrom the battery and the overall health of the charging system. The mainsensor for this is a current sense resistor integrated into the batterycable.

Traditionally, this is a flat resistor made of a MANGANIN resistiveelement terminated by copper pieces welded or brazed to each end of theresistive element. MANGANIN is an alloy typically 86 percent copper, 12percent manganese, and 2 percent nickel which provides low resistance.This flat resistor would be located at the end of the cable adjacent tothe connector to the battery and would be surrounded by supportelectronics encased in a potted container. Such a resistor may also beused in applications other than automotive application such as, but notlimited to, galvanic plating power supply cables, welding cables, andother applications.

Therefore, it is a primary object, feature, or advantage of the presentinvention to improve over the state of the art.

It is a further object, feature, or advantage of the present inventionto provide a resistor suitable for use in automotive and relatedapplications where the resistor is connected to a cable.

Yet another object, feature, or advantage of the present invention is toprovide a resistor which allows current sensing.

One or more of these and/or other objects, features, and advantages ofthe present invention will become apparent from the specification andclaims that follow.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a resistor includes asubstantially cylindrical resistive element having a resistance of lessthan about 1 mΩ, a substantially cylindrical first terminationelectrically connected to the resistive element, and a secondtermination electrically connected to the resistive element. Thesubstantially cylindrical first termination is hollow to allow foraccepting a connection such as from a battery cable. There may be one ormore sense leads attached to the resistor.

According to another aspect of the invention, a method of forming asubstantially cylindrical resistor is provided. The method includesforming a hollow cylindrical resistor body by rolling a flat sheetcomprising a resistive element and a first termination and a secondtermination joined on opposite ends of the resistive element.

According to another aspect of the invention, a method of forming asubstantially cylindrical resistor includes providing a first tube for afirst termination, providing a second tube for a second termination, andmagnetic pulse welding a resistive element between the first tube andthe second tube to thereby provide a substantially cylindrical resistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a cylindrical resistorof the present invention.

FIG. 2 is an exploded perspective view of one embodiment of thecylindrical resistor of the present invention.

FIG. 3 is a perspective view of the cylindrical resistor connected to abattery cable assembly of a vehicle.

FIG. 4 is a perspective view of the cylindrical resistor connected to abattery cable of a vehicle.

FIG. 5 illustrates a step in the process of forming a cylindricalresistor according to one embodiment.

FIG. 6 illustrates a step in the process of forming a cylindricalresistor according to one embodiment.

FIG. 7 illustrates a step in the process of making a cylindricalresistor according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is generally directed towards a cylindricalresistor and a method of making the cylindrical resistor. Thecylindrical resistor may be used in applications such as, but notlimited to, automotive applications, galvanic plating power supplycables, welding cables, and other applications. The cylindrical shapeallows the resistor to be integrated into a cable assembly in a morespace efficient manner and also allows insertion at any position alongthe length of the cable. Flexibility in positioning allows supportelectronics to also be positioned in a location closer to otherelectronics modules or at the battery terminal.

FIG. 1 illustrates a perspective view of one embodiment of a cylindricalresistor 10. The cylindrical resistor 10 includes a resistive element12. The resistive element 12 may be made from a cylindrical piece ofManganin wire, or other suitable resistive material. Each end of theresistive material is terminated with copper or another suitableconductive material to form the terminals 14, 16 of the resistor 10. Theterminals 14, 16 may be used to connect the resistor 10 to the cableassembly and carry the main current. These terminals 14, 16 are attachedto resistive element 12 by welding, brazing or crimping. The terminals14, 16 may be capable of attachment to a battery cable assembly bywelding, brazing or crimping. The geometry of the terminals may varybased on the particular application for which the cylindrical resistoris used and the present invention is not to be limited by the specificgeometry of the terminals shown.

Integral to the attachment of these terminations there are one or moresense leads 22, 24 attached to the terminals 14, 16. These sense leads22, 24 are used for connection to support electronics that require asense voltage input in proportion to the electrical current passingthrough the resistor 10. These leads 22, 24 may be an extension of theresistor terminal material or may be otherwise added such as throughwelding, brazing, crimping, or other means. The specific geometry ofthese sense leads may vary according to specific applications andenvironments and the present invention is not to be limited to thespecific geometries shown.

In one embodiment, the assembly of this shunt resistor 10 consists ofcopper tubes for the terminations 14, 16 and a piece of a substantiallycylindrical MANGANIN resistance wire as the resistive element 12. Theresistance wire is cut to a short segment. One end of the segment ofresistance wire is placed in the end of one copper tube and the two arejoined by a magnetic pulse weld that uniformly collapses the tube ontothe wire at such speed that a weld occurs. The other end of the Manganinwire resistive element is inserted into the end of the other copper tubeand joined by another magnetic pulse. Thus, a resistor such as resistor10 in FIG. 1 is formed.

The amount of unwelded resistive material between the ends of the twocopper tubes determines the blank resistance value. Adjustment of theresistance value can be made by a lathe, abrasion, or lasering operationthat reduces the diameter of the exposed MANAGANIN wire or by removingcopper from the end of each tube effectively lengthening the MANGANINresistive element. In addition, resistance can be adjusted by addingtermination material (such as copper or other conductive material) backto the resistive element such as by welding. At this point the open endsof the copper tubes are ready to accept further processing steps toconnect them to a cable assembly. Such as inserting cable 34 into theopen tube and magnetically pulse welding the two pieces together asshown in FIG. 4. This joint could also be made by soldering, crimping,brazing or other welding methods. A battery post clamp 30 having an end32 could also be inserted to one of the open tube ends and secured inplace as shown in FIG. 3. The battery post clamp may be secured bysoldering, crimping, brazing, or other welding methods.

FIG. 5 and FIG. 6 illustrate another embodiment of a cylindricalresistor. In this embodiment, the resistor utilizes a flat resistiveelement of Manganin, or other suitable resistive material, with copper,or other suitable conductive material, terminals welded to each end ofthe resistive material in the same fashion as may be used in fabricatingpower metal strip resistors such as disclosed in U.S. Pat. No. 5,604,477to Rainer, herein incorporated by reference in its entirety.

In FIG. 5, a flat sheet 39 is shown. The flat sheet 39 includes aresistive material 42, and terminal material 40. The terminal materialincludes a first portion 40A and a second portion 40B on opposite sidesof the resistive material 42. Sense lead 22 is electrically connected toand extends from the first portion 40A of the terminal material 40 whilesense lead 24 is electrically connected to and extends from the secondportion 40B of the terminal material 40.

The flat sheet 39 is rolled into a cylinder with the resistive material42 becoming a band that curves around the circumference of the cylinderas best shown in FIG. 6. The resistive material 42 and terminal material40 may have holes or slots 46 in specified areas to facilitate the rollforming process and to facilitate crimping to a cable. These slots 46may also be used to adjust resistance value and TCR. The material fromthese slots 46 may be separated from the main body on three sides yetleft connected on the fourth side to form a sense terminal integral tothe resistor material.

In another embodiment, shown in FIG. 7, the resistor is configured toallow for one termination 40A to be cylindrical for attachment to acable while the second termination area 40B has a flat terminal 48 whichmay include an aperture 50. The flat terminal 48 may be connected to abattery post or other stud mount connector.

Note that when the cylindrical resistor is hollow, the resistive elementmay be cooled by circulating a fluid through it. Cooling may bedesirable in certain environments.

The cylindrical resistors of the present invention have resistancevalues less than 1 mΩ and are designed to handle current of 200 A ormore. Thus, the cylindrical resistors are well-suited to automotiveapplications, battery monitoring applications, and related applicationswhere a low resistance is desired.

Therefore, a cylindrical resistor has been disclosed. The presentinvention contemplates variations in the size, shape, materials used,resistance, and other variations. Although various embodiments are shownand described, the present invention is not to be limited to thespecific embodiments shown.

1. A resistor comprising: a resistive element; a substantiallycylindrical first termination electrically connected to the resistiveelement; a second termination electrically connected to the resistiveelement; and wherein the resistive element, first termination and secondtermination are formed of a flat sheet rolled into a hollow andsubstantially cylindrical resistor body, the resistive material forminga band that curves around a circumference of the resistor body, andwherein at least the first termination forms a conductive tubeconfigured for axial connection to the cable.
 2. The resistor of claim 1further comprising a first sense lead electrically connected to thefirst termination and a second sense lead electrically connected to thesecond termination.
 3. The resistor of claim 1 comprising at least oneslot formed in the first termination to define a sense terminal.
 4. Theresistor of claim 3 further comprising at least one slot in theresistive element or the first termination to facilitate roll forming.5. The resistor of claim 1 wherein the resistive element is a metalstrip.
 6. The resistor of claim 1 wherein the first terminationcomprises a first conductive tube and wherein the second terminationcomprises a second conductive tube.
 7. The resistor of claim 1comprising at least one slot formed in the first termination tofacilitate crimping to the cable.
 8. The resistor of claim 1 wherein thesecond termination includes a flat terminal area.
 9. The resistor ofclaim 8 further comprising an aperture in the flat terminal area. 10.The resistor of claim 1 wherein a fluid or gas is circulated through theresistor to control temperature of the resistive element.
 11. A methodof forming a resistor configured for axial connection to a cable, themethod comprising: providing a resistive element disposed between afirst termination and a second termination, wherein the resistiveelement, first termination and second termination are formed of a flatsheet; and rolling the flat sheet to form a hollow and substantiallycylindrical resistor body, wherein the resistive material forms a bandthat curves around a circumference of the resistor body, and wherein atleast the first termination forms a conductive tube configured for axialconnection to the cable.
 12. The method of claim 11 wherein theresistive element has a resistance of less than 1 mΩ.
 13. The method ofclaim 11 further comprising adjusting resistance of the resistor bycutting the resistive element.
 14. The method of claim 11 furthercomprising adjusting resistance of the resistor by adding material tothe resistor body.
 15. The method of claim 14 wherein the material isadditional resistive material.
 16. The method of claim 14 wherein thematerial is additional termination material.
 17. The method of claim 11further comprising cutting slots in the flat sheet to facilitaterolling.
 18. The method of claim 11 further comprising attaching senseleads to the resistor body.
 19. A resistor, comprising: a resistiveelement; a first termination electrically connected to the resistiveelement; a second termination electrically connected to the resistiveelement; wherein the resistive element, first termination and secondtermination are formed of a flat sheet rolled into a hollow andsubstantially cylindrical resistor body, the resistive material forminga band that curves around a circumference of the resistor body; a firstsense lead electrically connected to the resistive element; and a secondsense lead electrically connected to the resistive element.